1. Technical Field
The present invention relates to a method for controlling adhesion of fried food products to process surfaces by using additives to control the interfacial tension of oil and by treating process surfaces contacting such food products. The treatment of surfaces relates to abrading, scoring or forming surfaces to reduce surface contact with dough and thereby reducing the interfacial tension between a surface and dough. The invention has particular application to cooking pre-formed dough snack pieces but can be applied to fried food products generally.
2. Description of Related Art
There are several types of prior art fryers typically used in the food industry for frying snack food products that require relatively even frying on all sides of the product. Generally, snack pieces, such as fabricated potato crisps, are formed from sheeting dough and cutting dough into discrete pieces (pre-forms) for treatment. Treatment involves cooking pre-forms in a fryer to produce cooked snack pieces. In general, these fryers cook product in a stream of hot oil.
In dough-sheeting operations, there are many process conditions that can affect the tendency of dough to stick to process surfaces (e.g. conveyor belts, molds and cooking surfaces). Of particular importance is interfacial tension between dough and process surfaces. Dough adheres to process surfaces as dough is cut, transported, and introduced into cooking oil. Excessive adhesion of dough can cause ineffective chip cutting, chip sticking, erratic behavior in a fryer, and under- or over-frying. Dough adhesion can be partly controlled by dough composition by the addition of emulsifiers such as lecithin with a particle size varying from 200 to 600 microns. However, dough composition cannot vary widely without drastically affecting the final product. Too much or too little adhesion can affect fried product taste, texture, appearance, quality variability, and control of package weight.
Control of dough adhesion is especially important as dough is introduced into cooking oil in fryers. Dough is initially denser than oil (oil having a lower specific gravity) when it is introduced to cooking oil on a conveyor. Ideally, as dough begins to cook, escaping gases cause the dough to release from conveyor or process surfaces. If the product is less dense than oil, buoyancy forces also exert an upward force that helps overcome adhesion forces. Adhesion forces keep dough attached to submerged conveyor surfaces.
However, buoyancy and other product-removing forces sometimes are not sufficient to overcome adhesion forces. Excessive adhesion leads to several undesirable results including dough residue buildup on conveyor surfaces, product of variable quality, wasted product, and process upsets. Excessive sticking or adhesion is a large source of inefficiency and waste during production. Excessive adhesion can even lead to a halt in production as equipment must be cleaned and re-initialized before production can continue.
In the current art, food processors rely on natural degradation of cooking oil in a fryer in order to ensure that food product fed to the fryer does not stick excessively to process surfaces such as conveyor belts. Some food products are cooked in fresh oil for 15 to 60 minutes before the cooking oil is in a condition such that the product does not stick excessively to cooking and conveying surfaces.
As one example, a prior art, single-mold form fryer for cooking snack products is shown in FIG. 1. A fryer assembly 100 receives uncooked snack pieces at an entrance area 102. After cooking, the snack products exit the fryer assembly 100 at an exit area 104.
Dough, formulated to produce the preferred snack pieces, is sheeted and formed into pre-forms before being cooked. In FIG. 1, the fryer assembly 100 processes pre-forms (not shown) through a form fryer with a top conveyor 120, a bottom entrance conveyor 130, and a bottom exit conveyor 140. The feeding segment is the top surface of the bottom entrance conveyor 130 between the input-side roller 132 and the submerged roller 134. The path of the bottom entrance conveyor 130 winds about several rollers 132, 134, 136, 138. After the bottom entrance conveyor 130 contacts the oil 152 in an entrance area 102, the snack pieces begin to fry.
Some degree of adhesion between a snack piece and conveyor surfaces 120, 130, 140 is necessary. Otherwise, dough pre-forms would slide uncontrollably along the downwardly-angled entrance conveyor 130 into the cooking oil 152. There must be adequate adhesion in order to prevent such sliding of pre-forms.
Contrarily, there should not be excessive adhesion. Consider, for example, the introduction of pre-forms into a single-mold form fryer as shown in FIG. 1. Ordinarily, upward forces due to cooking cause the pre-forms to separate from the bottom entrance conveyor 130, rise upwards, and contact the top conveyor 120 within a few seconds. Once the pre-forms contact the top conveyor 120, the bottom entrance conveyor 130 is no longer needed for the cooking of pre-forms. The bottom entrance conveyor 130 then passes by a peel plate or pan extension 158 before the bottom entrance conveyor 130 rotates about a submerged roller 134 and begins its return path to receive new pre-forms at the entrance area 102.
One purpose of a peel plate or pan extension 158 is to ensure that the flow of oil over the transition is as gentle as possible avoiding damage to dough product as it is transported toward the center of the fryer and exit conveyor 140. The gap between the peel plate 158 and bottom entrance conveyor 130 is prone to jamming if product fails to separate from the bottom entrance conveyor 130 before reaching the peel plate 158. Any gap between a moving process surface and another process surface may potentially cause a process upset if product fails to release from the surface to which it is attached or mated. Such process upsets are to be avoided.
Pre-form material is more likely to excessively adhere to a hot surface, such as a bottom entrance conveyor 130, if the surface is at a higher temperature than the pre-form. Contact with such hot surface is to be avoided even for a few seconds especially if the surface has not been coated with oil. If an excessive amount of pre-form material fails to disengage from the bottom entrance conveyor 130, the pre-form material may create a blockage at the peel plate or pan extension 158 and cause the process to halt as the non-released pre-forms prevent food product from reaching the exit conveyor 140.
In a typical fryer, the turn-over time of frying oil may be several hours depending on the quantity of product actually fried. The turn-over time is the amount of time it takes for an equivalent volume of cooking oil in the fryer to be replaced due to the loss of oil. The loss of oil is due in part to the oil adhering to, or being absorbed by, the food product. Fresh cooking oil must be added continuously or periodically to the fryer to replace lost oil. However, as disclosed herein, the use of fresh oil actually increases the likelihood that pre-forms do not release from the bottom entrance conveyor 130. The inventors have discovered that this phenomenon is due to a dramatic difference in the interfacial tension between fresh cooking oil and used cooking oil.
Consequently, a need exists to control the adhesion of dough pre-forms to facilitate the release of pre-forms into fryer oil. A need exists for a method to transport and process dough product wherein the product does not excessively stick or adhere to process surfaces. More specifically, a need exists for a system that allows dough product to be handled, transported and processed wherein interfacial adhesion of product to a surface is controlled to a desired level. Such a system is especially needed during startup of a dough fryer when interfacial adhesion is highest because of the presence of fresh cooking oil.